Protective ventilatory strategy should be applied to reduce ventilator-induced lung injury (VILI) after Lung Transplantation (LTx) or in case of acute respiratory failure requiring invasive mechanical ventilation. Neurally Adjusted Ventilatory Assist (NAVA) is an assisted ventilation mode in which respiratory support is coordinated by the electrical activity of the diaphragm (EAdi). Aim of the study is to assess the physiological relationship between neural respiratory drive, as assessed by EAdi, and tidal volume, driving pressure, and mechanical power, at different levels of ventilatory assist, in the absence of pulmonary vagal afferent feedback or during acute respiratory failure. Additional parameters will be collected: Pmus, Pocc, transpulmonary pressure etc.

Lung transplantation (LTx) is an important treatment option for select patients with end-stage pulmonary disease, while acute respiratory failure is a common disease among ICU patients. In the early period, following LTx or at the beginning of acute respiratory failure, a protective ventilatory strategy should be applied to reduce ventilator-induced lung injury (VILI). Neurally Adjusted Ventilatory Assist (NAVA) is an assisted ventilation mode in which neural inspiratory activity is monitored through the continuous recording of electrical activity of the diaphragm (EAdi) and then used to coordinate the respiratory support delivered by the ventilator.

NAVA, because of its intrinsic properties (proportionality between respiratory drive and level of assist, prevention of diaphragm atrophy), could allow the aforementioned ventilatory strategy, however it may require the integrity of the pulmonary vagal afferent feedback in order to avoid volutrauma. So, the aim of the study is the evaluation of the physiological relationship between EAdi and tidal volume, driving pressure and mechanical power, at different levels of ventilatory assist, in the absence of pulmonary vagal afferent feedback during early post-operative period after LTx and among critically ill patients affected by acute respiratory failure. Finally, additional parameters will be collected: Pmus, Pocc, transpulmonary pressure etc.

Inclusion Criteria:

• Age > 18 y.o.
• Admission to ICU for post-operative monitoring after LTx or acute respiratory failure needing invasive mechanical ventilation
• Presence of spontaneous breathing activity
• Sedation titrated to a target RASS between 0 and -2
• Written informed consent obtained

Exclusion Criteria:

• Contraindication to nasogastric tube insertion (gastroesophageal surgery in the previous 3 months, gastroesophageal bleeding in the previous 30 days, history of esophageal varices, facial trauma)
• Increased risk of bleeding with nasogastric tube insertion, due to severe coagulation disorders and severe thrombocytopenia ( i.e., INR > 2 and platelets count < 70.000/mm3)
• Severe hemodynamic instability (noradenaline > 0.3 μg/kg/min and/or use of vasopressin)
• Postoperative extracorporeal respiratory support (ECMO)
• Pre-operative reconditioning of the transplanted lungs by means of ex-vivo lung perfusion (EVLP)
• Lung retransplantation
• Failure to obtain a stable EAdi signal

none (open label)